Boiler

Abstract

According to the present invention, a boiler that performs combustion of any of a plurality of types of fuels includes a control unit that controls combustion amounts of a first fuel and a second fuel. The control unit is capable of controlling the combustion amount of the first fuel within a first range, and is capable of controlling the combustion amount of the second fuel within a second range that is different from the first range.

Description

Boiler

[0001] The present invention relates to a boiler. This application claims priority based on Japanese Patent Application No. 2025-027130 filed in Japan on February 21, 2025, the content of which is incorporated herein by reference.

[0002] When transporting gaseous fuels such as natural gas by ship, the gaseous fuel is stored in a tank in a cryogenic liquid state. At this time, since there is heat input from the surrounding environment to the liquefied gas storage tank, a certain amount of the gaseous fuel vaporizes inside the tank. Such vaporized gas is called boil-off gas (BOG). For example, in the case of liquefied natural gas (LNG), the global warming potential of methane, which is the main component of BOG, is about 25 times higher than that of carbon dioxide, and suppression of BOG emissions into the atmosphere is required. Therefore, BOG generated in liquefied natural gas carriers, etc., is re-liquefied by a re-liquefaction device or incinerated by an incineration device.

[0003] As a method of incinerating (burning) BOG, in addition to the method of burning it with a dedicated combustion device, a method of burning BOG with an auxiliary boiler that supplies steam is known (for example, Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2024-93886

[0005] In liquefied natural gas carriers, etc., it is necessary to safely and promptly process BOG generated from the liquefied natural gas tank during transportation and BOG (including inert gas mixed BOG) generated during the loading and unloading operations (gassing, gas-free) of liquefied natural gas without releasing it into the environment. However, the marine boilers installed to meet the steam demand on board are designed to have a maximum combustion amount of heavy oil, etc., that can supply the amount of steam used on board. Therefore, it was not possible to promptly burn a large amount of BOG that exceeded this maximum combustion amount of heavy oil, etc. Also, installing a large-capacity marine boiler that can burn a large amount of BOG was difficult because it not only caused a significant cost increase but also was restricted by the machinery room or the space on board.

[0006] This invention was conceived in view of the above circumstances, and its purpose is to provide a boiler that enables the combustion of heavy oil, etc., in a way that can optimally respond to the steam demands of the steam demanding section, while suppressing the release of hydrocarbon-containing gases such as BOG into the environment and enabling safe and rapid combustion of BOG, etc., without causing excessive cost increases.

[0007] To achieve the above objective, a boiler according to a certain aspect of the present invention is a boiler that burns any of a plurality of types of fuel, and includes a control unit that controls the combustion amounts of a first fuel and a second fuel, wherein the control unit can control the combustion amount of the first fuel within a first range and can control the combustion amount of the second fuel within a second range different from the first range.

[0008] With the above configuration, it becomes possible to burn each of several types of fuel at the optimal combustion rate, making it possible to burn each fuel at the appropriate combustion rate in a single boiler.

[0009] Preferably, the maximum combustion amount in the second range is set to a combustion amount that is a predetermined multiple of the maximum combustion amount in the first range, and the predetermined value is a value between 1.5 and 5.

[0010] With the above configuration, the first fuel and the second fuel can each be burned to their optimal maximum combustion rate, thus enabling the second fuel to burn quickly.

[0011] Preferably, the first fuel is a liquid fuel and the second fuel is a boil-off gas.

[0012] According to the above configuration, even when the first fuel is a liquid fuel and the second fuel is boil-off gas, each fuel can be burned to its optimal maximum combustion rate, thus enabling the rapid combustion of a large amount of BOG (boil-off gas).

[0013] Preferably, the control unit includes a combustion amount control storage unit that stores at least a maximum fuel amount control that enables the second fuel to be burned at the maximum combustion amount in the second range, and controls combustion based on the maximum combustion amount control of the second fuel stored in the combustion amount control storage unit.

[0014] With the above configuration, the second fuel is controlled based on the combustion amount control stored in the combustion amount control memory unit, so combustion can be performed in a second range, which is a maximum combustion amount different from the first range that is optimal for the combustion purpose of the second fuel.

[0015] Preferably, the minimum combustion amount in the second range is set to a combustion amount that is a specific multiple of the minimum combustion amount in the first range, which is smaller than the predetermined value.

[0016] According to the above configuration, a large turndown can be taken when burning the second fuel, and if the second fuel is BOG, BOG can be burned without releasing BOG into the environment even when the amount of BOG generated is small.

[0017] Preferably, the specified value is a value between 0.05 and less than 1.5.

[0018] With the above configuration, it becomes possible to burn only a relatively small amount of the second fuel.

[0019] Preferably, the minimum combustion amount in the second range is set to be smaller than the minimum combustion amount in the first range.

[0020] With the above configuration, it becomes possible to burn only a small amount of the second fuel.

[0021] This diagram illustrates the general configuration of a boiler system, including the boiler itself. It shows the overall structure of the boiler and its cross-sectional view along line A-A. The table shows an example of combustion using the boiler.

[0022] Embodiments of the present invention will be described below with reference to the drawings. First, the general configuration of a boiler system including the boiler according to this embodiment will be described with reference to Figure 1.

[0023] The boiler system shown in Figure 1 is installed on ships that transport gaseous fuels such as natural gas (LNG) as liquefied gas. The natural gas is cooled to below -160°C and stored in LNG tanks in a liquefied state.

[0024] Natural gas stored in LNG tanks is supplied to a vaporizer via a high-pressure pump and vaporized. The vaporized natural gas is supplied to the main engine. The exhaust gas generated by the main engine is supplied to the exhaust gas economizer in the boiler.

[0025] On the other hand, because LNG tanks receive heat from the surrounding environment, some of the natural gas in the tanks vaporizes into BOG (gas containing hydrocarbons vaporized from liquefied gas). The generated BOG can be supplied to a marine boiler and incinerated (combusted). Some of the generated BOG is cooled and reliquefied, some of which is returned to the tank, and the rest can be incinerated (combusted) in the boiler. In addition, the boiler burns heavy oil etc. (first fuel) stored in oil fuel tanks to meet the steam demand on board, and burns BOG etc. (second fuel) to process the BOG etc. generated in the LNG tanks. The steam generated in the boiler is used as steam in various load equipment on board the ship. Excess steam is sent to a condenser (heat exchanger), and the condensed drain is supplied to a drain tank and then supplied back to the boiler. Steam that cannot be processed in the condenser is discharged overboard. Figure 1 shows an example where heavy oil is burned to meet the steam demand on board the ship. However, to meet the steam demand on board the ship, natural gas supplied to the main engine may be used as the first fuel for boiler combustion.

[0026] Next, with reference to Figure 2, the general configuration of the boiler according to this embodiment will be described. Figures 2(a) and 2(b) show an example of an embodiment of a marine boiler, which is an example of a boiler according to the present invention. Figure 2(a) is an explanatory diagram of the overall structure, and Figure 2(b) is a cross-sectional view taken along line A-A in Figure 2(a).

[0027] A marine boiler includes a control unit that controls the combustion state, and controls the combustion amounts of the first fuel and the second fuel by at least one of step-value control and continuous control. Furthermore, the control unit includes a combustion amount control memory unit. The combustion amount control memory unit stores at least a maximum fuel amount control that makes the second fuel combustible at the maximum combustion amount in a second range, and preferably also stores a maximum combustion amount control that makes the first fuel combustible at the maximum combustion amount, a minimum combustion amount control that makes the first fuel combustible at the minimum combustion amount, and a minimum fuel amount control that makes the second fuel combustible at the minimum combustion amount in a second range. The control unit controls combustion based on the storage in the combustion amount control memory unit.

[0028] The marine boiler comprises a water-tube type composite boiler 7 that combines a combustion heat recovery water tube group 5, which connects an upper header (steam drum) 1 that functions as a steam chamber and a lower header (water drum) 2 that functions as a water chamber, with a combustion chamber 3 formed inside and connected by a large number of water tube groups 4, and a main engine exhaust heat recovery water tube group 6 that recovers the exhaust heat of the main engine by allowing the main engine exhaust gas to flow over the outer surface of the water tubes 4a to recover heat. The composite boiler 7 may also be further connected to an auxiliary engine exhaust heat recovery boiler (not shown) that recovers heat from the exhaust gas of auxiliary engines, so that the boiler water of the composite boiler 7 is in communication with it, and the water (mixture of steam and liquid) heated in the auxiliary engine exhaust heat recovery boiler is separated into gas and liquid in the upper header 1 of the composite boiler 7, and the steam is supplied to steam-using equipment. For example, a ship's engine is used as the main engine and a generator is used as the auxiliary engine.

[0029] In detail, the upper header 1 is formed in an annular shape, and the lower header 2 is formed in a cylindrical shape. The upper header 1 and the lower header 2 are connected by a group of water pipes 4, and the space between the upper header 1 and the lower header 2 is covered by a cylindrical outer wall 9.

[0030] A burner 11 is provided on the furnace side 10 of the annularly formed upper header 1. The burner 11 is connected to a first fuel supply line and a second fuel supply line (not shown) that supply fuel capable of burning a first fuel and a second fuel within a range from a minimum combustion amount to a maximum combustion amount (a first range and a second range, respectively). A first fuel adjustment unit (not shown) is provided on the first fuel supply line, and a second fuel adjustment unit (not shown) is provided on the second fuel supply line. The control unit adjusts the first fuel adjustment unit and the second fuel adjustment unit to control the amount of first fuel and second fuel supplied to the burner 11.

[0031] Water tubes 4a of the water tube group 4 connecting the upper header 1 and the lower header 2 are densely arranged to surround the portion that opens into the upper header 1, forming a cylindrical water tube wall 12 and creating a combustion chamber 3. Furthermore, water tubes 4b are densely arranged to communicate with the water tube wall 12 that forms the combustion chamber 3 and reach the outer perimeter wall 9, forming a water tube wall 14, and creating an exhaust gas flow path 15 that guides the combustion gas burned in the combustion chamber 3 to the combustion boiler exhaust gas outlet 16. An exhaust gas discharge duct for discharging exhaust gas overboard is connected to the combustion boiler exhaust gas outlet 16.

[0032] The combustion heat recovery water pipe group 5 consists of a burner 11 provided on the inside 10 of the furnace of the upper header 1, a combustion chamber 3 formed inside the cylindrical water pipe wall 12, and an exhaust gas passage 15 formed by the water pipe wall 14.

[0033] The water pipes 4c of the water pipe group 4 located outside the water pipe wall 14, which is composed of a water pipe wall 12 made up of water pipes 4a that form the combustion chamber 3 and water pipes 4b that form the exhaust gas passage 15, are arranged at predetermined intervals. The outer peripheral wall 9 covering the space between the upper header 1 and the lower header 2 is provided with a main engine exhaust gas inlet 17 and a main engine exhaust gas outlet 18. The main engine exhaust gas that enters the outer peripheral wall 9 from the main engine exhaust gas inlet 17 flows along the outer surface of the water pipes 4c of the water pipe group 4 and is discharged outside the outer peripheral wall 9 from the main engine exhaust gas outlet 18. A main engine exhaust gas introduction duct is connected to the main engine exhaust gas inlet 17 of the outer peripheral wall 9 to introduce the main engine exhaust gas into the outer peripheral wall 9, and a main engine exhaust gas discharge duct is connected to the main engine exhaust gas outlet 18 to discharge the main engine exhaust gas outside the ship.

[0034] The main engine exhaust heat recovery water pipe group 6 consists of a water pipe group 4 located outside the water pipe wall 12 that forms the combustion chamber 3 and the water pipe wall 14 that forms the exhaust gas flow path 15, and an outer peripheral wall 9 on which the main engine exhaust gas inlet 17 and the main engine exhaust gas outlet 18 are provided.

[0035] When using an auxiliary heat recovery boiler to recover heat from the exhaust gas of auxiliary machinery, the upper tube sheet partitioning the upper part of the water chamber of the auxiliary heat recovery boiler and the upper header 1 of the composite boiler 7 are connected by an upper connecting pipe 29 so that the water chamber of the auxiliary heat recovery boiler and the boiler water of the composite boiler 7 are in communication, and the lower tube sheet partitioning the lower part of the water chamber of the auxiliary heat recovery boiler and the lower header 2 of the composite boiler 7 are connected by a lower connecting pipe 30.

[0036] In a marine boiler configured in this way, the combustion gas from the burner 11 burning in the combustion chamber 3 of the combustion heat recovery water tube group 5 heats the water in water tubes 4a and 4b, and the main engine exhaust gas flowing into the outer wall 9 of the main engine exhaust heat recovery water tube group 6 heats the water in water tube 4c. The steam generated in the water tubes is separated into gas and liquid in the upper header 1 and supplied to steam-using equipment.

[0037] Next, with reference to Figure 3, the basic combustion control of the boiler according to this embodiment will be described. In the boiler according to this embodiment, when steam demand arises, a first fuel such as heavy oil is burned to generate steam, which is then supplied to the steam demand section. In addition, when incineration treatment of BOG or the like becomes necessary, a second fuel such as BOG is burned.

[0038] This embodiment describes an example of combustion control for a marine boiler in which heavy oil is burned as the first fuel shown in Figure 3 with stepped control in a range from low combustion amount (minimum combustion amount) to high combustion amount (maximum combustion amount) (first range), and LNG BOG is burned as the second fuel with continuous control in a range from minimum combustion amount to maximum combustion amount (second range). In this embodiment, the heavy oil adjustment unit (first fuel adjustment unit) includes a first heavy oil supply pipe (not shown) equipped with a first heavy oil shut-off valve and a second heavy oil supply pipe (not shown) equipped with a second heavy oil shut-off valve. The BOG adjustment unit (second fuel adjustment unit) includes a BOG shut-off valve and a BOG flow rate adjustment valve (not shown).

[0039] In conventional technology, the capacity of a marine boiler is selected according to the steam demand on board. For example, if a marine boiler with a maximum evaporation rate of 2,200 kg / h is installed and a steam demand arises on board, such as for tank cleaning, the marine boiler burns heavy oil in three positions based on the steam pressure inside the boiler: stop, low combustion (50%, 1,100 kg / h), and high combustion (100%, 2,200 kg / h), supplying the necessary steam to meet the steam load. When burning heavy oil at low combustion (50%), the control unit opens either the first or second heavy oil shut-off valve and controls the supply of heavy oil fuel from only one of the first or second heavy oil supply pipes. When burning heavy oil at high combustion (100%), both the first and second heavy oil shut-off valves are opened and the supply of heavy oil fuel from both the first and second heavy oil supply pipes. Unless otherwise specified, "○○ kg / h" refers to the amount of steam equivalent to the combustion rate, and "○○%" refers to the ratio of each combustion rate, with 100% representing the maximum possible combustion rate (amount of steam) when the first fuel is burned for the purpose of generating steam and supplying the steam to the steam demand section.

[0040] Furthermore, when it becomes necessary to incinerate BOG generated in an LNG tank, conventional marine boilers burn the BOG through continuous control from a minimum combustion rate (25%, 550 kg / h) to a maximum combustion rate (100%, 2,200 kg / h) based on the detection results of a BOG pressure detection unit installed in the BOG supply line that supplies BOG to the marine boiler. The control unit opens the BOG shut-off valve and adjusts the BOG flow rate control valve based on the BOG pressure detected by the BOG pressure detection unit, controlling the combustion rate within the range from a minimum combustion rate (550 kg / h) to a maximum combustion rate (2,200 kg / h). In other words, the maximum combustion rate when burning heavy oil and the maximum combustion rate when burning BOG were the same.

[0041] On the other hand, in this embodiment, the control unit of the marine boiler is equipped with a fuel quantity control memory unit that stores the maximum and minimum combustion amount controls for heavy oil (first fuel) and BOG (second fuel), respectively. For example, the combustion amount control memory unit stores in the first fuel combustion amount control memory unit a control for supplying heavy oil to the burner, in which, when burning heavy oil at low combustion (50%, 1,100 kg / h), either the first heavy oil shut-off valve or the second heavy oil shut-off valve is opened, and when burning heavy oil at high combustion (100%, 2,200 kg / h), both the first heavy oil shut-off valve and the second heavy oil shut-off valve are opened. Furthermore, the combustion amount control memory unit stores in the second fuel combustion amount control memory unit, as BOG supply control to the burner, information on the opening of the BOG shut-off valve, information on the opening degree of the BOG flow control valve that enables the supply of BOG at a maximum combustion amount greater than the maximum combustion amount of heavy oil (250%, 5,500 kg / h), and information on the opening degree of the BOG flow control valve that enables the supply of BOG at a minimum combustion amount (25%, 550 kg / h).

[0042] The control unit burns heavy oil in a stepped value control within a first range based on the memory stored in the combustion amount control memory unit, and burns BOG in a continuous control within a second range different from the first range. In other words, the combustion amount control unit comprises a first fuel combustion amount control unit and a second fuel combustion amount control unit. The first fuel combustion amount control unit performs heavy oil supply control and heavy oil combustion control using the information stored in the first fuel combustion amount control memory unit, and the second fuel combustion amount control unit performs BOG supply control and BOG combustion control using the information stored in the second fuel combustion amount control memory unit.

[0043] For example, when steam demand occurs inside the ship, the marine boiler burns heavy oil in the range from a low combustion amount to a high combustion amount (the first range) by three-position control of stop, low combustion (50%, 1,100 kg / h), and high combustion (100%, 2,200 kg / h) based on the steam pressure inside the boiler can, and supplies the steam required for the steam load. Further, when incineration treatment of BOG generated in the LNG tank becomes necessary, the marine boiler is based on the detection result of the BOG pressure detection unit provided in the BOG supply line that supplies BOG to the marine boiler, and burns BOG by continuous control in the range from the minimum combustion amount (25%, 550 kg / h) to the maximum combustion amount (250% (ratio to the maximum combustion amount of heavy oil), 5,500 kg / h) (the second range). In this case, the maximum combustion amount of BOG is 2.5 times the maximum combustion amount of heavy oil. Even when the marine boiler increases the BOG treatment capacity by setting the maximum combustion amount of BOG to 2.5 times that of heavy oil (the first fuel), the heat load on the water pipes can be kept within the allowable range.

[0044] According to the present embodiment, for the steam demand inside the ship, the first fuel can be burned in the first combustion range to supply steam with a boiler efficiency suitable for steam generation. Further, even when there is a requirement to incinerate a large amount of BOG generated from liquefied natural gas during transportation or BOG (including inert gas mixed BOG) generated during cargo handling operations (gassing, gas-free), for the incineration treatment of a large amount of BOG, it can be burned in the second range suitable for the incineration treatment of the second fuel, so that the incineration treatment of BOG can be carried out promptly, and the working time required for incineration and / or cargo handling can be shortened. Further, there is no need to install an excessive boiler for the steam demand inside the ship to incinerate BOG, and it is possible to avoid excessive equipment costs, running costs, and occupation of the limited installation space inside the ship.

[0045] In this embodiment, the value of the second range / first range (maximum combustion amount of BOG / maximum combustion amount of heavy oil) in the maximum combustion amount is preferably 1.5 or more and 5 or less, and from the viewpoint of heat load on burners and water pipes due to combustion and steam treatment, it is even more preferably 1.5 or more and 3 or less. Furthermore, in this embodiment, the value of the second range / first range (minimum combustion amount of BOG / minimum combustion amount of heavy oil) in the minimum combustion amount is set to be smaller than the value of the second range / first range (maximum combustion amount of BOG / maximum combustion amount of heavy oil) in the maximum combustion amount. This allows for the rapid combustion of large amounts of BOG, as well as combustion of small amounts of BOG without releasing it into the atmosphere. Therefore, the value of the second range / first range (minimum combustion amount of BOG / minimum combustion amount of heavy oil) in the minimum combustion amount is more preferably 0.05 or more and less than 1.5, and in particular, when the first fuel is heavy oil, it is preferable that it be less than 1 (the minimum combustion amount in the second range is smaller than the minimum combustion amount in the first range).

[0046] The present invention is not limited to the embodiments described above, and various modifications and applications are possible. Below, we will describe some modifications of the above embodiments that are applicable to the present invention.

[0047] In the above embodiment, a composite boiler comprising a combustion heat recovery water tube group 5 and a main engine exhaust heat recovery water tube group 6 was described as the boiler, but a marine auxiliary boiler consisting only of the combustion heat recovery water tube group 5 may also be used. In addition to boilers with water tubes, boilers with fire tubes may also be used. An example of a boiler with fire tubes is a fire-tube type composite boiler that combines a combustion boiler, in which the upper and lower ends of a cylindrical pressure-resistant shell plate are partitioned to form a water chamber, and a combustion furnace and fire tubes for carrying combustion exhaust gas are housed inside the water chamber, with a main engine exhaust heat recovery boiler housed inside fire tubes for carrying main engine exhaust gas.

[0048] In the above embodiment, an example of using liquid fuel as the first fuel has been described. However, gaseous fuels such as natural gas can also be used as the first fuel. Further, an example of incinerating the BOG of LNG in a marine boiler using heavy oil as the liquid fuel which is the first fuel has been described, but it is not limited thereto, and any boiler that burns any of a plurality of types of fuels may be used. For example, a boiler using kerosene or naphtha instead of heavy oil may be used. Further, in addition to the BOG of LNG, a boiler that burns BOG such as hydrogen may be used. Further, it is not limited to marine boilers, and land boilers may also be used.

[0049] In the above embodiment, the combustion control method described was that the combustion of heavy oil was controlled by a stepped value control and the combustion of BOG was controlled by continuous control. However, the invention is not limited to this, and the combustion of heavy oil and BOG may be controlled by continuous control. For example, heavy oil may be burned in a range of 50% to 100%, and BOG may be burned in a range of 25% to 250%. In this case, the heavy oil supply line (first fuel supply line) is equipped with a heavy oil shut-off valve and a heavy oil flow rate control valve (not shown), and the BOG supply line (second fuel supply line) is equipped with a BOG shut-off valve and a BOG flow rate control valve (not shown). The fuel combustion amount control memory unit stores, for example, the opening degree of the heavy oil flow control valve corresponding to the minimum combustion amount (50%, 1,100 kg / h) and maximum combustion amount (100%, 2,200 kg / h) of heavy oil in the first fuel combustion amount control memory unit, and the opening degree of the BOG flow control valve corresponding to the minimum combustion amount (25%, 550 kg / h) and maximum combustion amount (250%, 5,500 kg / h) of BOG in the second fuel combustion amount control memory unit. The control unit opens the heavy oil shut-off valve as heavy oil combustion control and adjusts the opening degree of the heavy oil flow control valve based on the steam load within the range from the opening degree corresponding to the minimum combustion amount to the opening degree corresponding to the maximum combustion amount of the heavy oil flow control valve stored in the first fuel combustion amount control unit, and performs continuous controlled combustion. Furthermore, the control unit, as part of the combustion control of the BOG, opens the BOG shut-off valve and adjusts the opening of the BOG flow control valve based on the BOG load (such as the BOG supply line pressure) within a range from the opening corresponding to the minimum combustion amount to the opening corresponding to the maximum combustion amount, which is stored in the second fuel combustion amount control unit, and burns the BOG through continuous control. For steam demand on board, the control unit burns heavy oil through continuous control within the range of maximum and minimum combustion amounts based on the steam load, and for BOG processing, it burns BOG within the range of maximum and minimum combustion amounts based on the BOG load. In addition, combustion using heavy oil as fuel may be performed through continuous control, while combustion using BOG as fuel may be performed through stepped value control.

[0050] Furthermore, although the above embodiment described an example in which both the maximum and minimum combustion amounts in the first and second ranges are different, it is sufficient for the maximum combustion amounts to be different in order to burn a large amount of BOG generated in a limited time, and for the minimum combustion amount to be different in order to continue burning a small amount of BOG generated. In other words, the present invention also includes cases where the minimum combustion amount is the same and only the maximum combustion amount is different, and cases where the maximum combustion amount is the same and only the minimum fuel amount is different.

[0051] Alternatively, the second fuel may be fixed combustion, where the maximum and minimum combustion amounts are the same. Fixed combustion is a combustion control with two positions: stop and burn, where the combustion amount during combustion is basically controlled to be constant. For example, heavy oil may be burned with continuous control in the range of 30% to 100% (2,200 kg / h) to supply to the steam demand section, and BOG may be incinerated as fixed combustion at 200% (4,400 kg / h). In this case, the BOG adjustment unit (second fuel adjustment unit) is equipped with a BOG shut-off valve and a BOG flow rate adjustment valve (not shown), and the opening degree of the BOG flow rate adjustment valve that results in a fixed combustion amount of 200% is stored in the second fuel combustion amount control storage unit of the combustion amount control storage unit.

[0052] Alternatively, the system may be configured so that the operator can switch the fixed combustion amount of the BOG using a changeover switch or the like. For example, if the fixed combustion amount of the BOG is set to 150%, 200%, and 250%, the second fuel combustion amount control storage unit of the combustion amount control storage unit stores at least the opening degree of the BOG flow control valve corresponding to when the fixed combustion amount of the BOG is 150%, 200%, and 250%.

[0053] Furthermore, the marine boiler may be equipped with a BOG flow rate adjustment unit that fixes the BOG flow rate to predetermined values ​​such that the BOG flow rate is 150%, 200%, and 250% of the combustion rate, and the second fuel combustion rate control memory unit may store control for flowing BOG through the BOG flow rate adjustment unit corresponding to the fixed combustion rate of BOG selected by the operator. The control unit performs combustion control of the BOG based on the combustion control information stored in the second fuel combustion rate control memory unit.

[0054] Furthermore, when burning BOG containing inert gas, or when the amount or composition of BOG fluctuates, co-firing of BOG and heavy oil (burning a predetermined amount of heavy oil together with the BOG) may be performed to ensure stable combustion of the BOG. ​​For example, heavy oil may be burned at a fixed combustion rate (880 kg / h), while the BOG may be burned at a predetermined combustion rate greater than the predetermined combustion rate of heavy oil (4,400 kg / h as the combustion rate of BOG without inert gas). The state at which the predetermined combustion rate of BOG can be burned can be adjusted, for example, by the opening degree of the BOG flow control valve.

[0055] If the opening of the BOG flow control valve is fixed so that the combustion rate of BOG without inert gas is 4,400 kg / h, the combustion rate when BOG and heavy oil are co-fired will change depending on the inert gas content. For example, the maximum combustion rate of BOG is 4,400 kg / h when BOG does not contain inert gas, and 2,200 kg / h when BOG contains 50% inert gas. The combustion rates when BOG and heavy oil are co-fired are 5,280 kg / h and 3,080 kg / h, respectively. If the maximum combustion rate of heavy oil to meet the steam demand on board is 2,200 kg / h, the combined maximum combustion rate of heavy oil and BOG when co-fired (5,280 kg / h) will be 240%.

[0056] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended to be included.

[0057] Furthermore, the present invention relates, for example, to the suppression of atmospheric emissions of boiler gas (BOG) generated from liquefied natural gas (LNG), and can contribute, for example, to Sustainable Development Goal 13 of the United Nations, "Take urgent action to combat climate change and its impacts." In addition, since BOG is burned by a boiler, the thermal energy generated by the combustion can be used in the steam demand section on board the ship, and can contribute, for example, to SDG Goal 7, "Ensure access to affordable, reliable, sustainable, and modern energy for all."

[0058] 1 Upper header 2 Lower header 3 Combustion chamber 4 Water tube group 4a, 4b, 4c Water tubes 5 Combustion heat recovery water tube group 6 Main engine waste heat recovery water tube group 7 Composite boiler 9 Outer wall 10 Inside of furnace 11 Burner 12, 14 Water tube wall 15 Exhaust gas flow path 16 Combustion boiler exhaust gas outlet 17 Main engine exhaust gas inlet 18 Main engine exhaust gas outlet 29 Upper connecting pipe 30 Lower connecting pipe

Claims

1. A boiler for burning any of several types of fuel, comprising a control unit for controlling the combustion amounts of a first fuel and a second fuel, wherein the control unit is capable of controlling the combustion amount of the first fuel within a first range and controlling the combustion amount of the second fuel within a second range different from the first range.

2. The boiler according to claim 1, wherein the maximum combustion amount in the second range is set to a combustion amount that is a predetermined multiple of the maximum combustion amount in the first range, and the predetermined value is a value of 1.5 or more and 5 or less.

3. The boiler according to claim 1, wherein the first fuel is a liquid fuel and the second fuel is a boil-off gas.

4. The boiler according to claim 1, wherein the control unit includes at least a combustion amount control storage unit that stores a maximum fuel amount control that enables the second fuel to be burned at the maximum combustion amount in the second range, and controls combustion based on the maximum combustion amount control of the second fuel stored in the combustion amount control storage unit.

5. The boiler according to claim 1, wherein the minimum combustion amount in the second range is set to a combustion amount that is a specific multiple of the minimum combustion amount in the first range which is smaller than the predetermined value.

6. The boiler according to claim 5, wherein the specified value is a value of 0.05 or more and less than 1.

5.

7. The boiler according to claim 1, wherein the minimum combustion amount in the second range is set to be smaller than the minimum combustion amount in the first range.

Images